Making a site expand? Masking?

Ok i’ll try to explaint his best i can,
i wanted to have my preloader load nd then disappear when done loading, then the white background frame of the layout to expand upwards and downwards and then the site content to appear on it. how would i get it to expand? wouldnt i have to do something with masking?

i’m also a noob at flash lol and dont know how to mask, how would i do it? lol
is there a tutorial somewhere? i looked and i couldnt find now